1. Field of the Invention
The present invention relates to an in-line strainer disposed in a pipe line for spraying a liquid such as an agricultural chemical solution and the like, so as to be coaxial with the pipe line.
2. Description of the Background Art
An example of conventional in-line strainers as described above is shown in FIG. 11A. An in-line strainer 61A shown in the diagram includes a housing 62 which includes a cylindrical-shaped main body case 63 having an inflow port 66 arranged at one end of the cylinder, and a main body lid 64 fitted to the other end of the cylinder of the main body case 63 in a sealed manner. Inside the housing 62, a valve seat 95 is formed in the vicinity of the inflow port 66, and a valve element 92 for opening or closing the valve seat 95 is installed. A cylindrical-shaped strainer element 83A is disposed between an inner circumference surface of the main body case 63 and the valve element 92 so as to be coaxial with the housing. The strainer element 83A is held by a holding member 90 which is pressed by the lower surface of the main body lid 64 and which allows a liquid to pass therethrough. The valve element 92 is urged, by a coil spring 91 disposed between the valve element 92 and the holding member 90, toward a direction in which the valve seat 95 is closed. The inflow port 66 is connected to, for example, a hose which is connected to a pump, and an outflow port 67 is connected to a chemical solution spraying pipe having a nozzle.
In the in-line strainer 61A, when an agricultural chemical solution flows from the inflow port 66, the agricultural chemical solution pushes the valve element 92 to open the valve seat 95, and thereby flows into the strainer element 83A. The agricultural chemical solution passes through the strainer element 83A from its inside to its outside, so as to filter impurities such as dirt, gravel, and the like, and is discharged, through the holding member 90, from the outflow port 67 to the chemical solution spraying pipe. Such an in-line strainer that causes the agricultural chemical solution to pass through the strainer element from its inside to its outside is disclosed in U.S. Pat. No. 5,490,868, for example.
On the other hand, another example of an in-line strainer of the type described above is shown in FIG. 11B. An in-line strainer 61B shown in the diagram includes a housing 62 similar to that included in the above-described in-line strainer 61A. This housing 62 does not include a valve seat 95, but includes a cylindrical-shaped strainer element 83B. The strainer element 83B has a first end which is closed by four crimped portions 94 which are formed in a circumferential direction of the strainer element 83B, and has a second end which is open. The open second end of the strainer element 83B is held by an inner circumferential surface of a main body lid 64 and by a coil spring 93, and is connected to an outflow port 67.
In the in-line strainer 61B, an agricultural chemical solution flowing from an inflow port 66 to a main body case 63 passes through the strainer element 83B from its outside to its inside so as to filter impurities, and is discharged from the outflow port 67 to a chemical solution spraying pipe.
When the strainer element 83A or 83B is clogged during spraying operation, spraying force is decreased, and an amount of spraying is also decreased, resulting in unsatisfactory spraying operation. Thus, the in-line strainer 61A or 61B needs to be disassembled on the spot to remove impurities. In this case, an operator needs to stop an on-off valve which is disposed at an upstream side from the in-line strainer 61A or 61B, and also needs to remove the main body lid 64 from the main body case 63 in order to extract the strainer element 83A or 83B. That means that a whole of the pipe line from the pump to the nozzle is opened in the middle of the spraying operation, and thus there may be a case where a large amount of agricultural chemical solution is drained out of the main body case 63. Moreover, impurities on the extracted strainer element 83A or 83B need to be removed by using a brush or the like. However, impurities which are firmly stuck cannot be removed easily. Particularly, in the case of the strainer element 83A, since the impurities are accumulated on an inner surface of the element, it is difficult to remove the impurities by using a brush.
On the other hand, when a mesh of the strainer element is coarse, impurities having a large diameter pass through the strainer element, which leads to a possibility that the nozzle at the downstream side is clogged with the impurities. Thus, a strainer element having a relatively fine mesh is used, and accordingly, impurities ranging from fine-grain ones to large-gain ones are captured by the strainer element. Thus, the strainer element needs to be cleaned very frequently.